Components working with acoustic waves, for example SAW components (SAW=Surface Acoustic Wave), GBAW components (GBAW=Guided Bulk Acoustic Wave) or BAW components, (BAW=Bulk Acoustic Wave), can be used in radio-frequency circuits, e.g., in bandpass filters. For this purpose, they comprise a piezoelectric material and also electrode structures. The electrode structures convert an RF signal into acoustic waves that propagate in the piezoelectric material, however, electrode structures also convert acoustic waves into RF signals. In general, it is desirable to avoid leaky wave losses and the excitation of interference modes, and to obtain an electroacoustic coupling coefficient κ2 high enough for the bandwidth of the application, and a smallest possible temperature coefficient of frequencies.
Bandpass filters working with acoustic waves can be used, for example, as reception filters or as transmission filters, for example in a duplexer. Such bandpass filters are intended to have a low insertion loss in the passband, a high stop band suppression outside the passband, and also a high performance. Furthermore, they are intended to be producible with a small component size and in a cost-effective manner.
International Patent publication No. WO 2005/036744 A1, for example, discloses a component working with acoustic waves comprising an LiNbO3 substrate (LiNbO3=lithium niobate). Finger-shaped electrode structures are arranged between the substrate and an SiO2 layer.
The requirements made of components working with acoustic waves constantly increase. In particular, the usable frequency range of a passband is intended to be as wide as possible and that of the transition range from the passband to the stop band is intended to be as narrow as possible. The stop band suppression is intended to be improved, and the temperature coefficient of frequencies (TCF) is intended to be minimized. The temperature coefficient of frequencies designates the temperature dependence of the frequency-dependent attenuation characteristic of a filter. The undesirable effects of the temperature coefficient are temperature-dependent shifts of, for example, the passbands of bandpass filters.
Furthermore—in accordance with the continuous trend toward miniaturization—corresponding components are intended to be able to be made smaller than known components.